Ancient Megacities Were Displaced Due To A Changing Climate: Study

The Bronze Age Indus civilization, which spanned across northwest India and Pakistan, flourished for thousands of years and mysteriously declined as some type of development forced these ancient people to abandon the mega-cities they had constructed.

A newly published paper in the journal Geology has asserted that climate change may be behind this abrupt change in the Indus way of life.

“We think that we now have a really strong indication that a major climate event occurred in the area where a large number of Indus settlements were situated,” said David Hodell, an earth science professor at Cambridge University in the United Kingdom. “Taken together with other evidence from Meghalaya in northeast India, Oman and the Arabian Sea, our results provide strong evidence for a widespread weakening of the Indian summer monsoon across large parts of India 4,100 years ago.”

This theoretical change in the monsoon rains would have come at the peak of the ancient Asian civilization.

“The major cities of the Indus civilization flourished in the mid-late 3rd and early 2nd millennium BC,” said Cameron Petrie, an archaeologist at Cambridge. “Large proportions of the population lived in villages, but many people also lived in ‘megacities’ that were 80 hectares (197 acres) or more in size.”

“They engaged in elaborate crafts, extensive local trade and long-ranging trade with regions as far away as the modern-day Middle East,” Petrie added. “But, by the mid 2nd millennium BC, all of the great urban centers had dramatically reduced in size or been abandoned.”

To reach their conclusion, the multidisciplinary team used a radioactive analysis of the oxygen isotopes found in snail shells buried within the sediments of an ancient lakebed. The analysis showed a reduced summer monsoon rainfall at the same time that other evidence points to the beginning of the Indus de-urbanization. From 6,500 to 5,800 years ago, the freshwater lake that existed at Kotla Dahar converted to a smaller lake showing a weakening of the Indian native summer monsoon. Another abrupt weakening took place 4,000 years ago – drying up the lake completely.

Petrie said these drops in rainfall would have severely impacted the Indus people living at the time.

“Houses were arranged on wide main streets and narrow alleyways, and many had their own wells and drainage systems,” he said. “Water was clearly an integral part of urban planning, and was also essential for supporting the agricultural base.”

“At around the time we see the evidence for climatic change, archaeologists have found evidence of previously maintained streets start to fill with rubbish, over time there is a reduced sophistication in the crafts they used, the script that had been used for several centuries disappears and there were changes in the location of settlements, suggesting some degree of demographic shift,” he added.

“We estimate that the climate event lasted about 200 years before recovering to the previous conditions, which we still see today, and we believe that the civilization somehow had to cope with this prolonged period of drought,” Hodell said.

“It is essential to understand the link between human settlement, water resources and landscape in antiquity, and this research is an important step in that direction,” Petrie concluded. “We hope that this will hold lessons for us as we seek to find means of dealing with climate change in our own and future generations.”